The primitive linear heart tube of the fruit fly Drosophila melanogaster provides a unique model system to study the genetic control mechanisms of the heart development. Although during last decade studies of cardiac morphogenesis using this model animal identified important genes for cardiac development, many cardiogenic genes remain to be identified in order to gain insight into the genetic control mechanism of cardiac morphogenesis. Using information obtained Drosophila genome sequencing and and RNAi (RNA interference) technology as a new strategy for blocking gene function we have initiated genome-wide screening of regulatory genes that are involved in Drosophila heart development. For the screen, we have injected dsRNA into embryos from transgenic flies that harbor beta-galactosidase transgene that is mainly expressed in cells of cardiogenic lineage. By monitoring change in expression pattern of beta-galactosidase transgene and morphology of the heart in the injected embryos we could easily identify potential cardiogenic genes. About 6,000 dsRNAs were prepared in vitro using DNAs obtained from the unigene set (BDGP), and we have also established that 21-nucleotide synthetic RNA duplexes can mediate RNAi in the Drosophila embryo. We initially microinjected a pool of dsRNAs (3 genes per pool) into embryos (40-60 embryos) and then assayed again individual dsRNA from a positive pool. We have finished screening of 5,800 genes that cover approximately 40% of all Drosophila genes and discovered many genes (total 133 genes) that potentially play roles in Drosophila cardiac development. Both novel genes and known genes with mammalian homologues and with previously undescribed functions in heart development have been identified. From studies of genes identified from this screen we found that the cardiac tube is segmentally patterned, which was shown by down-regulation of paired and ftz-F1. We also found that homeotic genes such as abd-A are required for heart patterning. Genes encoding transcription factors and signaling molecules have been identified, and characterization of those cardiogenic genes are now under way by using both transgenic fly lines that we have generated and potential mutants for the identified genes. Because the genetic control mechanisms of the embryonic cardiac development of the Drosophila are well conserved in mammalian heart development, identifying cardiogenic regulatory genes in Drosophila should help us understand the genetic control mechanism of the mammalian cardiac morphogenesis.